U.S. Pat. No. 5,918,502 discloses an article of footwear which has a piezoelectric element in the sole. The piezoelectric element is pre-formed in an arcuate shape. When the wearer of the footwear walks or runs the force of the sole impacting the ground causes the piezoelectric element to deform. This generates electricity. However, it requires a special type of curved piezoelectric element, which is expensive and difficult to manufacture.